Cassette elevator for use in a modular article processing machine

ABSTRACT

Improved handling of multi-wafer cassettes in automated wafer processing machines is accomplished by means of an improved cassette elevator. The design of the cassette elevator is such that the receiver/sender portion of the wafer processing machine can be easily configured to accommodate single or multiple cassette elevators served by a single wafer loading spatula without increasing the width of the receiver/sender units. In addition, an automatic tilt feature of the cassette elevator substantially reduces the likelihood of wafer breakage during the cassette loading and unloading operation.

FIELD OF THE INVENTION

The present invention relates, in general, to an automated articleprocessing machine which accepts articles to be processed from acassette and returns processed articles to a cassette. Moreparticularly, the invention relates to an improved cassette elevator foruse in such an article processing machine. The cassette elevator isparticularly suited for use in wafer processing machines used insemiconductor device manufacture.

BACKGROUND OF THE INVENTION

The need for increased yield and throughput in manufacture in general,and in the manufacture of semiconductor devices in particular, hasdriven the development and use of more highly automated articleprocessing machines. An example of this trend is the increased use ofcassette-to-cassette wafer processing machines in the manufacture ofsemiconductor devices. Such machines accept a cassette containing aplurality of semiconductor wafers, remove the wafers from the cassetteand process them in a more or less automated fashion and return thewafers to the original cassette or to a second cassette.

An important part of any cassette-to-cassette wafer processing machineis the cassette elevator. The cassette elevator generally comprises aplatform which carries the cassette and some means for moving theplatform in a vertical direction. Since semiconductor wafers are carriedin the cassette in a vertical stack, the precisely controlled verticalmotion of the cassette elevator provides access to each of the wafersindividually. In other words, the elevator is serially indexed so thateach wafer in the cassette is brought into a position in which it can beremoved from or inserted into the cassette by some wafer transfermechanism which operates in a primarily horizontal fashion.

An example of a wafer transfer mechanism which operates in conjunctionwith the cassette elevator is a spatula transfer mechanism. A spatulatransfer mechanism operates in a substantially horizontal plane andinserts a spatula capable of carrying a wafer into the open front sideof the cassette. A wafer is removed from the cassette by indexing thecassette elevator to a position in which the spatula can be insertedimmediately below that wafer. The spatula is inserted and the cassetteelevator is indexed downward a small distance to rest the wafer on thespatula rather than on the cassette supports. The spatula is thenremoved, carrying the wafer.

A primary shortcoming of present cassette elevators is their inabilityto be configured in single or multi-elevator systems withoutsubstantially increasing the "footprint" and complexity of the system.In other words, prior art cassette elevators may only be positioned sideby side with an individual spatula for each elevator. It has beenimpossible to place multiple cassette elevators front to back and servethem with a single spatula.

A further shortcoming of current cassette elevators concerns the methodof loading and unloading cassettes onto the elevator platform.Typically, this operation is performed with the cassette platform in ahorizontal position, this makes it relatively easy for wafers to bejostled out of the open front side of the cassette during the loadingand unloading operation.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide animproved cassette elevator for use in a modular article processingmachine.

Yet a further object of the present invention is to provide a cassetteelevator for use in an automated semiconductor wafer processing machinewhich can be arranged in a multi-elevator, front to back system and beserved by a single spatula.

Still a further object of the present invention is to provide a cassetteelevator for use in an automated semiconductor wafer processing machinewhich substantially reduces the likelihood of wafer breakage during thecassette loading and unloading operations.

A particular embodiment of the present invention comprises a cassetteelevator for use in a modular automated semiconductor wafer processingmachine. A cassette platform which is adapted to carry standardmulti-wafer cassettes is carried in a cantilever fashion by a lead screwand rail arrangement. The lead screw is driven by a motor whose angularposition is precisely determinable. This provides the necessary verticalpositioning of the cassette. The cantilever arrangement between thecassette platform and the lead screw portion of the elevator allows aspatula to pass unimpeded under the platform when the elevator is in itsupper-most position. Therefore, a second elevator located behind thefirst elevator may be served by the same spatula. This allows theelevator and spatula system, commonly referred to as a sender/receiver,to be easily configured in single or multi-cassette systems withoutincreasing the overall width of the wafer processing machine. Sincefloor space in the ultra clean wafer fabrication areas in which waferprocessing machines typically operate is so expensive, this ease ofreconfiguration within substantially the same footprint is a significantadvantage.

A further feature of this particular embodiment of the present inventionprovides an automatic rearward tilt of the cassette platform when theelevator is in its fully-raised position. That is, when the elevator isin the position in which loaded cassettes are placed on and removed fromthe cassette platform, the operator is forced to tilt the loadedcassettes in such a fashion that jostling the wafers out of the openfront side of the cassette is extremely unlikely. As the elevator islowered to the position in which wafers are loaded and unloaded by thespatula, the cassette platform returns automatically to its horizontalposition.

These and other objects and advantages of the present invention will beapparent to one skilled in the art from the detailed description belowtaken together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a modular wafer processing machine;

FIG. 2 is a simplified plan view of a wafer transport system for use ina machine such as shown in FIG. 1;

FIGS. 3A-3H are a series of schematic diagrams illustrating a method ofwafer transport in a machine such as shown in FIGS. 1 and 2;

FIG. 4 is a schematic diagram of a machine state counter for use in amachine such as shown in FIG. 1;

FIG. 5 is an exploded perspective view of an elevator and load locksystem for use in a machine such as shown in FIG. 1;

FIGS. 6A and 6B are top and side views, respectively, of a cassetteelevator for use in a machine such as shown in FIG. 1;

FIG. 7 is a cross-sectional view of a load lock apparatus for use in amachine such as shown in FIG. 1;

FIGS. 8A and 8B are top and side views respectively of a pass throughcassette for use in a load lock apparatus such as shown in FIG. 7;

FIG. 9 is an exploded perspective view of a vacuum transport portion ofa machine such as shown in FIG. 1;

FIG. 9A is a partial cross-sectional view of the vacuum transport systemof FIG. 9;

FIG. 10 is a cross-sectional view of a magnetic drive apparatus for usein a vacuum transport system such as shown in FIG. 9;

FIG. 11 is a cross-sectional view of a combined wafer stage and reactorelectrode for use in a vacuum transport system such as shown in FIG. 9;

FIG. 12 is a simplified cross-sectional view of a service sealarrangement for use in a machine such as shown in FIG. 1; and

FIG. 13 is a simplified cross-sectional view on an enlarged scale of analternate service seal arrangement.

DETAILED DESCRIPTION OF THE INVENTION

The manufacture of semiconductor devices is normally carried out at thewafer level. That is, disk-like wafers of semiconductor materialcomprising a relatively large number of individual devices proceed as awhole through the various manufacturing steps before being separatedinto individual die which each contain a single device, such as amicroprocessor. The need for higher yield manufacturing processes leadsto more automated wafer processing machines which can process a largernumber of wafers per hour and to machines which process those wafers ina cleaner environment. FIG. 1 is a detailed perspective view of such awafer processing machine which embodies a number of improvements overthe prior art. The particular machine shown in FIG. 1 is a two-headplasma etching apparatus. That is, the machine has two plasma processingstations. The actual wafer processing takes place in first and secondplasma reactors 11 and 12. Reactors 11 and 12 are supplied with RF powerby RF power supplies 13 and are evacuated by means of vacuum manifold14. A further system which is not seen in this view provides reactivegases to reactors 11 and 12. Wafers to be processed are loaded into themachine by means of a multi-wafer cassette which is loaded onto elevator15. From there the wafers are transferred to an internal multi-wafercassette in vacuum load lock 16. A vacuum transport system 17 moveswafers from load lock 16 into reactors 11 and 12 for processing. Whenprocessing is complete, vacuum transport system 17 moves wafers to asecond load lock 18 and they are finally removed and placed into amulti-wafer cassette on elevator 19. The remainder of the waferprocessing machine comprises a plurality of electronic modules 20 andcontrollers 21 for monitoring and modulating the flow of the reactivegases. In addition, a display 22 is typically provided so that anoperator can monitor the overall state of the machine. As now expectedin the art, a complex machine such as this is generally controlled byone or more microprocessors, rather than fixed logic, which easilyaccommodates display 22.

As is described in detail with reference to each of the figures below,the overall design philosophy of the wafer processing machine shown inFIG. 1 is modularity. For instance, the machine can be configured withone, two, or more plasma reactors without significantly altering theoverall layout or wafer transport method. In addition, elevators 15 and19 and the associated wafer transfer apparatus are designed so that boththe input and output ends of the machine may have one or two elevators.Various other aspects and improvements of the wafer processing machineshown in FIG. 1 will be apparent from the remainder of the drawings anddescription.

Referring now to FIG. 2, the overall wafer transport system is shown ina simplified plan view. A multi-wafer cassette is entered into thesystem on elevator 15. Multi-wafer cassettes are familiar in the art andare typically closed on three sides and open on the fourth. Wafers areremoved and replaced via the open side and are supported on the threeclosed sides. A spatula 24 removes individual wafers from the cassetteon elevator 15 and places them in an internal cassette in load lock 16.As is familiar in the art, spatula 24 moves only horizontally and wafersare placed on and removed from spatula 24 by vertical movements ofelevator 15 and the internal cassette. For instance, the internalcassette would be positioned vertically so that spatula 24 carrying awafer will move into the appropriate wafer slot. Once spatula 24 is sopositioned, the internal cassette is indexed upwardly a small distanceto lift the wafer off spatula 24. Spatula 24 is then removed, leavingthe wafer in the internal cassette. Once the internal cassette isloaded, load lock apparatus 16 is cycled. That is, load lock 16 isclosed and sealed, the atmosphere is removed therefrom and then loadlock 16 is opened to connection with vacuum transport system 17.

Vacuum transport system 17 comprises first and second shuttle plates 25and 26, which move in a horizontal direction on guide rails 27, andchucks 28 and 29 which serve both in the wafer handling scheme and asthe lower electrode in plasma reactors 11 and 12, respectively. Inoperation, shuttle plate 25 is moved to its extreme left and a waferfrom the internal cassette in load lock is placed on tines 30. Becauseof mechanical coupler arm 31, shuttle plate 26 simultaneously moves toits extreme left and any wafer which had been on chuck 28 is placed ontines 32. Similarly, any wafer which had been on chuck 29 is placed ontines 33. The next phase of operation involves moving shuttle plates 25and 26 to their extreme right, whereby a wafer on tines 30 is placed onchuck 28, a wafer on tines 32 is placed on chuck 29 and a wafer on tines33 is placed in the outgoing load lock 18. Next, shuttle plates 25 and26 are moved to the positions shown in FIG. 2. Next, chucks 28 and 29are raised to carry their respective wafers into the plasma chambers andthe plasma process is performed. Finally, chucks 28 and 29 are loweredand vacuum transport system 17 moves new wafers into position to beprocessed. When all of the wafers have been transferred to outgoing loadlock 18, that load lock is cycled and spatula 34 removes the wafers tothe multi-wafer cassette on outgoing elevator 19.

If the wafer processing machine is configured as a single head machine,the apparatus of FIG. 2 will be precisely the same except thateverything to the right of dotted line 35 and coupling arm 31 isremoved. In such a system the wafer transport method is relativelysimple. Once wafers are in load lock 16, they are serially removed byshuttle plate 25, processed and returned to load lock 16. Thus, in thisconfiguration, load lock 16 and elevator 15 serve both input and outputfunctions.

In the two-head configuration shown in FIG. 2, the rightmost shuttleplate 26 carries two sets of tines, 32 and 33, while the leftmostshuttle plate 25 carries only a single set of tines, 30. Thisrelationship can be reversed without affecting the overall transportscheme.

FIGS. 3A-3H schematically illustrate the wafer transport method used inthe two-head configuration shown in FIGS. 1 and 2. Initially, six wafersto be processed are in a multi-wafer cassette on elevator 15 (FIG. 3A).Following the wafer transfer and load lock cycle steps, wafers 1 through6 are in the internal cassette in load lock 16 and are accessible by thevacuum transport system (FIG. 3B). One cycle of the vacuum transportsystem; i.e.: a full left movement followed by a full right movement;moves wafer number 1 onto chuck 28 and leaves wafers 2 through 6 in loadlock 16 (FIG. 3C). One more cycle of the vacuum transport system moveswafer 1 onto chuck 29 and wafer 2 onto chuck 28. At this point, chucks28 and 29 are raised to close the plasma reactors and the plasma processis performed (FIG. 3D). Next, chucks 28 and 29 are lowered and thevacuum transport system is put through one cycle. This results in wafer1 being transferred to load lock 18, wafer 2 being transferred to chuck29 and wafer 3 being transferred to chuck 28, leaving wafers 4 through 6in load lock 16 (FIG. 3E). One more cycle of the vacuum transport systemplaces wafer 2 into load lock 18, wafer 3 onto chuck 29 and wafer 4 ontochuck 28. Once again, chucks 28 and 29 are raised and the plasma processis performed (FIG. 3F). In steps not shown in FIG. 3, wafers 3 and 4 aremoved into load lock 18, wafers 5 and 6 are moved onto chucks 28 and 29and processed and are subsequently moved into load lock 18. This leavesall of the six wafers in load lock 18 (FIG. 3G), which is cycled priorto removing wafers 1 through 6 to output cassette 19 (FIG. 3H).

The described wafer transport scheme lends itself particularly well to amodular wafer processing machine. The ability to use each of the chucksas a wafer holding platform during the transfer operation allows the useof a multi-head, in line system without the added complexity of partialwafer processing in each of the chambers. the extension of this schemeto a three-head wafer processing machine is straightforward. The primarydifference being that three cycles of the vacuum transport system willintervene between each processing step.

In any complex electromechanical machine such as is described herein,the difficulty of recovering from a power failure or similar accident atsome point in the midst of the operation of the machine may arise. Thatis, the microprocessor which controls the function of each of thetransport motors, the pneumatic valves and other devices in the systemmust know the state of each of those devices when it is restarted in themiddle of processing. the problem is complicated by the fact that thevarious electromechanical, pneumatic and other systems are notmechanically interconnected; i.e. one cannot simply advance to the nextmachine state. FIG. 4 is a schematic diagram of a method for providingthe necessary information. Each time main microprocessor 40 completes anoperation, such as moving an elevator or raising a chuck, a signal issent to motor 41 which increments a counter 42 by one. Thus, the numberdisplayed by counter 42 uniquely identifies the state the machine was inwhen it completed the last step prior to the malfunction. When power isrestored, a machine operator keys in the number displayed on counter 42,which is then used by main microprocessor 40 to determine its state andto continue processing. This deceptively simple solution to the problemof determining the machine's state is much superior to a systemrequiring a sensor or sensors for each moveable component. It is alsopossible, of course, to make counter 42 machine-readable so that nooperator intervention is required to identify the machine's state atpower up.

Referring now to FIG. 5, the elevator-load lock portion of the apparatusis described with reference to an exploded perspective view thereof. Inautomated wafer processing machines, this portion of the machine istypically referred to as a sender/receiver unit. The configuration shownin FIG. 5 has two elevators 45 and 46, respectively. Elevators 45 and 46are shown in a simplified version in FIG. 5 and are shown in greaterdetail in FIGS. 6A and 6B. In general, each elevator comprises a frame47, a pair of guide rails 48, a lead screw 49, a motor 50 coupled tolead screw 49, a carrier 51 riding on guide rails 48 and driven by leadscrew 49 and a cassette platform 52. Motors 50 are of the type which arecapable of rotation in accurately predetermined steps. Thus, thevertical position of cassette platforms 52 can be controlled veryprecisely. This is necessary to achieve wafer transfer between themulti-wafer cassette and spatula 24. Carrier 51 supports cassetteplatform 52 in a cantilever fashion so that when elevator 45 is in itsfully raised position it does not interfere with spatula apparatus 53.This feature allows the use of multiple elevators arranged front-to-backand served by a single spatula. Although not shown in FIG. 5, cassetteplatforms 52 include pins, grooves and/or rails to aid in positioningthe multi-wafer cassette to insure accurate loading and unloading.

Spatula apparatus 53, which is shown away from its normal position forclarity, comprises a frame 55, a pair of guide rails 56, a lead screw57, a motor 58 attached to frame 55 and coupled to lead screw 57, acarrier 59 guided by guide rails 56 and driven by lead screw 57 and aspatula 24 attached to carrier 59. The cantilever arrangement betweenspatula 24 and carrier 59 is such that frame 55 of spatula apparatus 53mounts on the opposite wall of the machine from frames 47 of elevators45 and 46. To facilitate the allowance for single or dual elevatorconfigurations, spatula apparatus 55 is made long enough to serve thedual elevator configuration. In the single elevator configuration,spatula apparatus 53 is simply mounted in a more rearward position.Changing from a single to a dual elevator configuration simply involvesbolting in the second elevator, moving the spatula apparatus forward andaltering the programming of the microprocessor controller.

Load lock apparatus 16 comprises bulkheads 61, a dual motion mechanicalfeedthrough apparatus 62, a housing 63, sealing plates 64, a lower belljar 65, an upper bell jar which cannot be seen in this view and aninternal passthrough cassette which also is not seen in FIG. 5. A slot66 in each of the bulkheads 61 provides access between load lock 16 andthe vacuum transport system when the upper bell jar is raised. Sincevacuum load lock apparatus 16 is designed to function on either theinput or the output end of a modular wafer processing machine, sealingplates 64 are used to seal the unused slot 66. A more detaileddescription of load lock apparatus 16 is given with reference to FIG. 7,below.

In broad outline, the operation of the apparatus of FIG. 5 is asfollows. A multi-wafer cassette is placed on each cassette platform 52.One of the elevators, say elevator 45, is lowered to a position in whichspatula 24 can be inserted under the first wafer. Also, the upper belljar is lowered to seal off the vacuum transport system, lower bell jar65 is lowered and the internal passthrough cassette is lowered. As willbe apparent from the discussion below, dual motion feedthrough 62 driveseach of these movements. Spatula 24 is inserted under the first wafer inthe cassette and elevator 45 is moved down a very small distance toplace the wafer on spatula 24. Spatula 24 is then moved rearward toplace the wafer in the internal cassette. The internal cassette is thenmoved up a very small distance to pick up the wafer from spatula 24.This wafer transfer operation is repeated until each of the availableslots in the internal passthrough cassette is filled. Next, the internalcassette is raised, as is lower bell jar 65, thus completely sealingload lock apparatus 16, which is pumped down to approximately the samevacuum level as the vacuum transport system. Next, the upper bell jar israised to provide the vacuum transport system with access to theinternal cassette. At this point wafer transfer to the processing headsand processing can commence.

FIGS. 6A and 6B are top and side views, respectively, of a particularelevator apparatus 68. In both FIGS. 6A and 6B, the cassette platformwhich carries the multi-wafer cassette has been removed to showunderlying detail. The frame of elevator apparatus 68 comprises a lowermounting plate 69, an upper mounting plate 70 which is not shown in FIG.6A, a cover plate 71 which is not shown in FIG. 6B, a pair of guiderails 72 and a lead screw 73. Cover plate 71 extends between lowermounting plate 69 and upper mounting plate 70 and serves to isolate theparticle producing mechanism of elevator 68 from the wafers. A motor 74is mounted on lower mounting plate 69 and coupled to lead screw 73. Acarrier plate 75 rides guide rails 72 and is driven by lead screw 73. Acantilevered portion 76 of carrier plate 75 extends around cover plate71 and provides a mounting point for a pivot pin 77. A platform carrier78 is pivotally carried on pivot pin 77 at a front edge thereof and,thus, is connected to carrier plate 75 by a double cantilever. The edgeof carrier plate 78 at which it is mounted to pivot pin 77 is the edgewhich faces the load lock apparatus. A cam 79 is mounted on cover plate71 and a cam follower 80 is mounted on platform carrier 78. Finally, aspring 81 biases carrier plate 78 to a horizontal position.

As carrier plate 75 is moved to its uppermost position by motor 74 andlead screw 73, cam follower 80 contacts cam 79 and forces platformcarrier 78 to a rearwardly inclined position. Of course, when carrierplate 75 is in a lower position in which cam follower 80 does notcontact cam 79, spring 81 maintains platform carrier 78 in a horizontalposition. This automatic tilting feature of elevator 68 significantlyreduces the likelihood of wafer breakage. When multi-wafer cassettes arebeing loaded onto conventional elevators, it is relatively easy tojostle wafers out of the roughly vertical cassette and break them.However, with elevator 68 the cassette platform is in a rearwardlyinclined position when the multi-wafer cassette is being loaded, i.e.when elevator 68 is in its uppermost position. Thus, the operator isforced to tilt the multi-wafer cassette backwards, thus insuring thatthe wafers will not jostle out of the open front side of the cassette.The cassette platform typically includes a backstop to increase thestability of the cassette on the platform in the tilted position. Theother major feature of the elevator illustrated in FIGS. 6A and 6B isthe cantilever relationship between the drive mechanism and the elevatorplatform. As discussed above, this feature allows the spatula apparatusto pass under the first elevator in the dual elevator arrangement.

FIG. 7 is a detailed cross sectional view of load lock apparatus 16 asshown in FIG. 5. As discussed with reference to FIG. 5, bulkheads 61with slots 66 provide mounting and access to the vacuum transportsystem. Dual motion mechanical feedthrough 62 actuates the internalcomponents of the load lock apparatus while providing a vacuum seal. Theload lock itself comprises lower bell jar 65, fixed sealing plate 92 andupper bell jar 93. Lower bell jar 65 is moved from its lowered positionas shown to a raised position in which it seals to sealing plate 92 byactuator 90. Actuator 90 may be, for instance, a pneumatic cylinder andpiston. Mounting device 91, which couples actuator 90 to lower bell jar65 is arranged so that lower bell jar 65 can slide in the directionperpendicular to the plane of FIG. 7. This feature allows the easyremoval of lower bell jar 65 to remove pieces of broken wafers. AnO-ring 96 provides the necessary seal between lower bell jar 65 andsealing plate 92.

Sealing plate 92, which may be advantageously made of stainless steel toprovide an adequate seal over a long lifetime, has a generallyrectangular aperture to allow the passage of passthrough cassette 94. Aplurality of holes 97 are arranged along the inner perimeter of thisaperture. Holes 97 are coupled to a vacuum system so that the load lockcan be pumped down when both lower bell jar 65 and upper bell jar 93 aresealed to sealing plate 92.

Upper bell jar 93, which is shown in its raised position, issubstantially similar to lower bell jar 65. Upper bell jar 93 includesan O-ring 98 for providing a seal to sealing plate 92.

Internal passthrough cassette 94, which is discussed in more detail withreference to FIGS. 8A and 8B below, serves to receive a number ofunprocessed wafers from the cassette on the elevator and to hold themuntil they are retrieved by the vacuum transport system. On the outputend of the wafer processing machine, passthrough cassette 94 serves toreceive processed wafers from the vacuum transport system and hold themuntil they are transferred to the output cassette.

Both upper bell jar 93 and passthrough cassette 94 are moved in avertical direction by dual motion feedthrough apparatus 62. As isapparent, the positions of lower bell jar 65 and upper bell jar 93 shownin FIG. 7 would never occur simultaneously in the normal operation ofthe load lock apparatus. When upper bell jar 93 is in the raisedposition shown, lower bell jar 65 is sealed against sealing plate 92.This maintains the integrity of the vacuum in the vacuum transportsystem and allows access through slot 66 to wafers in passthroughcassette 94. On the other hand, when lower bell jar 65 is in its loweredposition, as shown, upper bell jar 93 is sealed against sealing plate 92and passthrough cassette 94 is also lowered to a position below sealingplate 92. In this position, upper bell jar 93 maintains the integrity ofthe vacuum in the vacuum transport system and passthrough cassette 94may be loaded and/or unloaded by the spatula. The third normal positionof the load lock is with both upper bell jar 93 and lower bell jar 65sealed to sealing plate 92. In this position, the load lock may becycled to or from the level of the vacuum in the vacuum transport systemand atmospheric pressure. As was discussed above, holes 97 in sealingplate 92 are coupled to the systems which perform this cycle. As will beapparent to one skilled in the art, it is also possible to perform somemanufacturing processes in the load lock when it is in the fully closedstate. In other words, holes 97 may be used to vent reactive gases intothe closed load lock. Once the desired process is complete, the loadlock is evacuated via holes 97. This capability allows more than oneprocess to be run in a single machine, thereby improving overallthroughput and reducing costs.

Turning now to dual motion mechanical feedthrough apparatus 62, this ismost easily described by referring to an outer actuator 100 and an inneractuator 101. Outer actuator 100 moves upper bell jar 93 between itsraised and lowered positions and also carries inner actuator 101. Inneractuator 101 raises and lowers passthrough cassette 94. Therefore, whenouter actuator 100 is lowering upper bell jar 93, the entire inneractuator 101 and passthrough cassette 94 are also being lowered.

Outer actuator 100 is, in essence, a pneumatic cylinder and pistonarrangement. A cylinder 102, which has end caps 103 and 104, contains apiston 105. Air inlets 106 and 107 in end caps 103 and 104,respectively, are coupled to a pneumatic control system which providesthe differential pressure across piston 105 necessary to move it. Inaddition, a guide pin 108 which is affixed in end caps 103 and 104 andon which piston 105 slides, serves to avoid misalignment between piston105 and cylinder 102. A stop 109 mounted on end cap 103 serves torestrict the motion of piston 105 in the downward direction. An outersleeve 110 is affixed to piston 105 and is sealed where it passesthrough end caps 103 and 104 by O-rings 111 and 112, respectively. Outersleeve 110 is mechanically coupled through block 113 and collar 114 toupper bell jar 93. Thus, when the air pressure at air inlet 107 isgreater than that at air inlet 106, piston 105 moves downward carryingouter sleeve 110 and upper bell jar 93. Similarly, when the pressure atair inlet 106 is greater than that at air inlet 107, piston 105 movesupward carrying outer sleeve 110 and upper bell jar 93. Since inneractuator 101 is carried within outer sleeve 110, its motion also followsthat of piston 105.

Inner actuator 101 comprises a motor 115, a lead screw 116, a nut 117,and sliders 118, 119 and 120. Motor 115 turns lead screw 116 whichimparts a linear motion to nut 117. Nut 117 is mechanically coupled toslider 118 which, in turn, is coupled to sliders 119 and 120. Therefore,rotary motion of lead screw 116 is translated into linear motion ofsliders 118, 119 and 120. Slider 120 is mechanically coupled topassthrough cassette 94. Sliders 118, 119 and 120 slide within an innersleeve 121 which is carried within outer sleeve 110. Inner sleeve 121moves with outer sleeve 110. The arrangement described allows motor 115to precisely position passthrough cassette 94 as is required for thetransfer of wafers.

While outer actuator 100 and inner actuator 101 impart the necessarymotions to upper bell jar 93 and passthrough cassette 94, the requiredvacuum seal is provided by sealing apparatus 125. Sealing apparatus 125primarily comprises lower plate 126, collar 127 and diaphrams 128 and129. As is apparent, lower plate 126 is sealed via housing 63 andbulkheads 61 to the vacuum transport system. Collar 127 is sealed at oneend to lower plate 126 and at the other to outer sleeve 110. Diaphram128 is captured at its outer edge between lower plate 126 and collar127. At its inner edge it is captured between block 113 and collar 114.Thus, diaphram 128 provides a vacuum seal for the apparatus which movesupper bell jar 93. Diaphram 129 is captured at its outer edge betweencollar 114 and inner sleeve 121. At its inner edge it is capturedbetween slider 119 and slider 120. Thus, diaphram 129 provides a vacuumseal for the apparatus which moves passthrough cassette 94. An air inlet130 and a bleed hole 131 are used to provide a slight positive pressureon the upper sides of diaphrams 128 and 129 so as to maintain theirshapes.

FIGS. 8A and 8B are bottom and side views, respectively, of passthroughcassette 94. The primary feature of passthrough cassette 94 whichdistinguishes it from previous wafer cassettes is that it must beaccessible to wafer transport mechanisms moving in perpendiculardirections. That is, the spatula which transfers wafers from thecassette on the elevator to passthrough cassette 94 operates in onedirection and the vacuum transport system operates in a substantiallyperpendicular direction. This requires that wafers be supported onlyfrom the four corners of passthrough cassette 94. To this end, eachwafer carrying stage of cassette 94 comprises four corner posts 135which each carries an arm 136. Arms 136 extend from corner posts 135toward the center of cassette 94. Toward the inner end thereof, arms 136are stepped to preclude gross misalignment of a wafer within cassette94. Each corner post 135 is coupled to the one above it and finally totop plate 137 by crews or other appropriate means. In this manner, apassthrough cassette 94 can be readily assembled from simple parts tocarry as many wafers as is desired by simply adding another layer ofposts 135 and arms 136. Of course, the room available in the load lockplaces an upper limit on the size of cassette 94.

FIG. 9 is an exploded perspective view of vacuum transport system 17 asit would be configured in a single-head wafer processing machine. Vacuumtransport system 17 is comprised of three major components. First, acontainment vessel 140 serves as the primary vacuum containment. Second,a magnetically driven transport system 141 serves to transport wafersfrom passthrough cassette 94 to the chuck. Finally, chuck assembly 142serves to remove wafers from transport system 141 and to raise them intoposition to be processed. In addition, a portion of chuck assembly 142serves as a lower electrode of the plasma processing chamber.

Containment 140 primarily comprises a box 145 and an upper plate 146.Box 145 has bulkheads 147 on either end thereof to provide coupling tothe elements of the machine on either end. For instance, in a singlehead configuration, the leftmost bulkhead 147 would be coupled tobulkhead 61 of load lock 16 and the rightmost bulkhead 147 would besealed with sealing plates 148. Box 145 also contains baffles 149 whichserve to isolate the particle generating portions of transport system141 from the wafers.

Wafer transport system 141 comprises a pair of drive motors 150 whichare typically mechanically coupled to ensure identical motion, a pair ofrails 27 which are located within box 145 behind baffles 149, a pair ofsliders 152 which ride on rails 27 and a shuttle plate 25 attached tosliders 152. As is apparent from FIG. 9, each of the rails 27 iscomprised of a large rail and a small rail. However, the smaller railsserve merely to improve the mechanical rigidness of the system and maybe ignored for further purposes. As will be more apparent from thedescription of FIG. 10 below, motors 150 are mounted outside box 145.Shuttle plate 25 carries a pair of tines 30 which enter passthroughcassette 94 and carry wafers therefrom.

Chuck assembly 142 comprises a dual motion mechanical feedthrough 155, amounting bell 156 and chuck 28. As will be apparent from the descriptionof FIG. 11 below, dual motion mechanical feedthrough 155 issubstantially identical to feedthrough 62 used on load lock 16. Thisidentity substantially reduces manufacturing costs and reduces thenumber of parts which must be kept in inventory. Mounting bell 156mounts to the bottom of box 145 and chuck 28 is disposed within box 145.Pins 157 can be raised to a position above the upper surface of chuck 28and lowered to a position below that surface by dual motion feedthrough155. A wafer which is carried by tines 30 is positioned over pins 157while they are lowered below the surface of chuck 28. Pins 157 are thenraised to lift the wafer off of tines 30. Pins 157 are typically loweredafter tines 30 are removed to allow the wafer to rest on the uppersurface of chuck 28. At this point chuck 28 is raised by dual motionfeedthrough 155 to seal with upper plate 146 and place the wafer withinthe plasma processing chamber. The entire process is reversed to removethe wafer from the processing chamber. Of course, in a multi-headconfiguration, the wafer would not be picked up by tines 30 afterprocessing but would be picked up by tines reaching into box 145 fromthe adjacent shuttle plate.

FIG. 9A is a partial cross-sectional view of the apparatus of FIG. 9which more readily illustrates the mechanism of wafer transfer betweentines 30 and pins 157. The plane of FIG. 9A is perpendicular to thedirection of motion of shuttle plate 25. Tines 30 are somewhat lowerthan shuttle plate 25 and are supported therefrom in such a manner thata wafer 154, which has been lifted from tines 30 by pins 157, can passbetween tines 30 and shuttle plate 25. In other words, shuttle plate 25and tines 30 pass around wafer 154 when it is supported on pins 157.This feature minimizes the amount of horizontal movement of shuttleplate 25 necessary to achieve the wafer transfer.

FIG. 10 is a detailed cross sectional view of a portion of the magneticdrive system 141. Walls 158 are the end walls of box 145. Tube 159 istypically a stainless steel tube which comprises one of the larger railsof the transport system. Both larger rails are of this type. Tube 159 issealed at walls 158 to preserve the integrity of the vacuum system.Thus, the interior of tube 159 can be open to the atmosphere withoutinterfering with the vacuum system. A lead screw 160 is coaxial withtube 159 and is mounted in a bearing 161 at one end and has a pulley 162at the other to couple it to one of the motors 150. A pair of guidewires 163 are affixed inside tube 159 beside lead screw 160. A nut 164is driven by lead screw 160 and guided by guide wires 163. A pair oftoroidal magnets 165 are carried by nut 164. Magnets 165 are disposed ateither end of nut 164. Slider 152 rides the outside of tube 159, that isinside the vacuum system, and carries a toroidal magnet 166. The fieldsof magnets 165 and 166 are arranged so that magnet 166 remainssubstantially centered between magnets 165. Thus, as lead screw 160moves nut 164 along the length of tube 159, slider 152 is moved alongthe outside of tube 159. This arrangement allows the primaryparticle-producing portions of the drive mechanism to be located outsidethe vacuum containment system. This arrangement also allows motors 150to be located outside the vacuum containment system for easy service.

FIG. 11 is a detailed cross sectional view of dual motion feedthrough155 and chuck 28. As is apparent from a comparison, feedthrough 155 isnearly identical to feedthrough 62 of FIG. 7. Identical referencenumerals are used in the two figures to identify identical parts.Briefly, an outer actuator 100 comprises a pneumatic cylinder 102 havingend caps 103 and 104 and a piston 105. Air inlets 106 and 107 couple thepneumatic control lines to actuator 100. An outer sleeve 110mechanically coupled to piston 105 is sealed where it passes through endcaps 103 and 104 by O-rings 111 and 112, respectively. A guide pin 108serves to keep piston 105 from cocking in cylinder 102. In thisembodiment of the dual motion feedthrough, there is no stop to restrictthe motion of piston 105 (see stop 109 in FIG. 7). Outer sleeve 110 iscoupled through block 131 and collar 168 to chuck 28. Therefore, motionof piston 105 is translated to motion of chuck 128.

Inner actuator 101 comprises motor 115, lead screw 116, nut 117 andsliders 118, 119 and 169. Slider 169 is coupled through plate 172 topins 157. Sliders 118, 119 and 169 slide within inner sleeve 121 whichis carried with outer sleeve 110. Therefore, rotary motion of lead screw116 driven by motor 115 is translated into vertical motion of pins 157.As is described above, pins 157 serve to transfer wafers to and fromtines 30 of shuttle plate 25 and chuck 28.

A vacuum sealing apparatus 125 comprises collar 127, bottom plate 170which is a part of sealing bell 156, outer diaphram 128, inner diaphram129, air inlet 130 and bleed hole 131. Outer diaphram 128 and innerdiaphram 129 serve to provide vacuum seal for outer actuator movement100 and inner actuator movement 101, respectively. Air inlet 130 andbleed hole 131 serve to maintain positive pressure behind diaphrams 128and 129, respectively.

A stop 171 which is part of sealing bell 156 serves to limit thedownward movement of chuck 28 and thereby precisely determines its fullylowered position. This is necessary to effect transfer of wafers betweenthe shuttle plate and the pins.

Vacuum sealed couplings 173 provide the necessary RF power to chuck 28.A similar set of vacuum sealed couplers which is not visible in thissection provide cooling water to chuck 28.

A series of O-rings 174, 175 and 176 provides the necessary seals forchuck apparatus 142. O-ring 174 provides a seal between sealing bell 157and vacuum containment box 145. O-ring 175 provides a seal between chuck28 and upper plate 156 of vacuum containment 140 when chuck 28 is in itsfully raised position. O-ring 176 provides a vacuum seal betweenelectrode portion 177 of chuck 28 and the bottom of the plasma reactorapparatus which is not shown in FIG. 11. This is described in moredetail with regard to FIGS. 12 and 13 below. Electrode portion 177 ofchuck 28 is affixed to chuck 28 with a plurality of bolts 178 around itsperiphery. This allows interchangeability of electrode portion 177 tobetter configure chuck apparatus 142 for a particular process withoutsubstantial changes to the remainder of the system.

FIG. 12 is a simplified cross sectional view illustrating one embodimentof the sealing arrangement between chuck 28, upper plate 146 of vacuumcontainment 140 and plasma chamber 180. Sealing valve 156 and dualmotion feedthrough 155 provide the necessary seal for the aperture inthe bottom of vacuum containment box 145 through which the chuckapparatus is passed. O-ring 175 provides a seal between chuck 28 andupper plate 146 when chuck 28 is in its fully raised position. O-ring176 provides a seal between chuck 28 and bottom plate 182 of reactor180. O-ring 181 provides a seal between bottom plate 182 and top plate146. To electrically isolate side wall portions 183 of reactor 180 fromelectrode portion 177 of chuck 28, bottom plate 182 is typically made ofa ceramic or other insulating material. When chuck 28 is in its fullyraised position as shown in FIG. 12, plasma reactor 180 may be removedfrom top plate 146 for servicing without disturbing the vacuum in thevacuum transport system. This allows service to reactor 180, replacementof electrode portion 177 of chuck 28 and similar measures to beundertaken without contaminating the vacuum transport system with air.O-ring 176 is necessary to prevent reactive gases in plasma reactor 180from being drawn into the vacuum transport system during processing.O-ring 181 is necessary to preserve the vacuum in the entire system whenchuck 28 is lowered for wafer transfer purposes.

FIG. 13 is a cross sectional view on an enlarged scale of an alternateembodiment of the service seal arrangement discussed with reference toFIG. 12. In this case, O-ring 175 and the step necessary to carry it areremoved from chuck 28. An inflatable seal 185 carried in top plate 146provides the necessary seal between plate 146 and chuck 28. O-rings 176and 181 and electrode 177 are substantially the same as shown in FIG.12. The primary purpose of this alternate embodiment of the service sealarrangement is to provide for a larger electrode 177 while maintainingthe overall diameter of chuck 28.

I claim:
 1. In a wafer processing machine, a cassette elevatorcomprising:a cassette platform adapted to carry a multi-wafer cassette;a carrier plate, said cassette platform being pivotally coupled to saidcarrier plate in a cantilever fashion; and drive means coupled to saidcarrier plate for vertically positioning said carrier plate and cassetteplatform, said drive means being positioned to allow passage of aspatula under said cassette platform when said cassette platform is in afully raised position.
 2. A cassette elevator according to claim 1further comprising:means for tilting said cassette platform when saidcassette platform is in said fully raised position and for restoringsaid cassette platform to a substantially horizontal orientation whensaid cassette platform is in a lowered position.
 3. A cassette elevatoraccording to claim 1 further comprising:cover means for substantiallyisolating said drive means from said multi-wafer cassette.
 4. A cassetteelevator according to claim 1 further comprising:cover means forsubstantially isolating said drive means from said multi-wafer cassette;a pivot pin carried by said carrier plate; a platform carrier pivotallycarried at a leading edge thereof by said pivot pin, said platformcarrier carrying said cassette platform; a cam carried on said covermeans; and a cam follower carried on said platform carrier, said cam andcam follower being arranged to pivot said platform carrier about saidpivot pin thereby imparting a tilt to said cassette platform as saidcassette platform is moved to its fully raised position.
 5. The cassetteelevator as set forth in claim 1 and further comprising:a second carrierplate; a second cassette platform, adapted to carry a multi-wafercassette, pivotally coupled to said second carrier plate in a cantileverfashion, a second drive means coupled to said second carrier plate forvertically positioning said second carrier plate and second cassetteplatform; wherein said second cassette platform is positioned relativeto the first cassette platform so that said spatula can accessmulti-wafer cassettes on either cassette platform.
 6. A cassetteelevator comprising:a carrier plate; drive means for verticallypositioning said carrier plate; a pivot pin attached at one end to saidcarrier plate and extending horizontally therefrom; a platform carrierattached at one edge thereof to said pivot pin and extendingapproximately horizontally therefrom; said platform carrier beingrotatable about said pivot pin; and means for tilting said platformcarrier only when said platform carrier is adjacent the upper end of itstravel and for maintaining said platform carrier at a substantiallyhorizontal position when at locations other than adjacent the upper endof its travel.
 7. The cassette elevator as set forth in claim 6 whereinsaid means for tilting includes:cover means for separating said drivemeans from said platform carrier; a cam attached to said cover means;and a cam follower, attached to said platform carrier, for engaging saidcam and imparting a tilt to said platform carrier.